Having spent quite many years in the engineering services with regards to flow products in downstream manufacturing plants, i am a fir...
Having spent quite many years in the engineering services with regards to flow products in downstream manufacturing plants, i am a firm believer that an effective preventive maintenance program in Oil and Gas, Refining, Petrochemicals, Energy plants can reduce frequent downtime and increase plant productivity. Some of the basic steps with regards to Valves and Controls would be to regularly cycle the valves so as to avoid any deposition or corossion of sealing faces. To learn more on the basic guidelines to selection criteria of valves for a particular application, Click Here to read my earlier post.
It is very essential that the drain valves are flushed out from time to time whenever possible. Repacking valves regularly over a pre-determined period can eliminate scoring of stems and seizure of valve. Torquing the gland nuts to the manufacturer specified value can drastically reduce the occurrence of hard to operate valves. As far as relief valves are concerned an annual trend of set pressure adjustment and testing of these valves can eliminate failure in operation of relief valves. To Learn more on Selection criteria and Sizing of Pressure relief valves, Click Here to read my earlier post.
Control valves being the most intelligent of the lot also need attention. Poor control valve performance is the single biggest source of process variability. Inadequate valve performance can often result in process cycling, high process time constant and excessive dead time resulting in poor control loop performance. Repacking and torquing of gland nuts are also an essential element with regards to control valves. Control valve maintenance falls into two categories: routine maintenance and response maintenance. To learn more about the basic guidelines and applications of Control Valves, Click Here to read my earlier post.
Routine maintenance or preventative maintenance involves checking the control valves on a predefined schedule. Response or breakdown maintenance is required when valve performance has seriously degraded and the process is having a dramatic negative impact on process performance. During preventative maintenance the obvious mechanical issues are attended to and then the valve is bench set and stroked. Checking the stroke typically involves operating the valve over its full range in 25% intervals. This approach does not adequately identify performance problems such as valve dead band. Additionally, the testing performed on the bench or in the line during shutdown does not reflect the valve performance under operating conditions. Process operating pressures can greatly impact the valves operation. To Learn more on the different causes of failures in Control Valves, Click Here to read my earlier post.
Some of the failure in pneumatic actuators can be largely due to wear and tear of soft parts, which many operations people overlook until it has actually failed. Such failures can be drastically reduced by following an annual trend of maintenance which may include stroke checking and proactively replacing soft parts, with factory approved repair kits and instrument accessories if any before failure.To learn more on the basic guidelines and selection criteria of Actuators, Click Here to read my earlier post.
To Learn more on Control Valves for Process plants, We reccommend you read the following books. Click on the links below to BUY ON AMAZON
"Process control for practitioners" by Jacques F Smuts
"Troubleshooting Process Plant Control" by Norman P Lieberman
"Control Valve Primer" by Hans D Baumann